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BUGS2
The BU Graduate Student Seminar








05/20/09 Luca D'Alessio: "Hubbard model for spin-1 bosons"
	 (SCI 328 4:00pm)
Abstract:
The Hubbard model for spin-1 bosons brings together the 
superlfuid-Mott insulator transition and magnetism. 
It is a theoretically interesting and challenging problem. 
Moreover, both the ferromagnetic and the anti-ferromagnetic cases 
can be realized in a lab using cold atoms in an optical lattice.
The anti-ferromagnetic case has a very rich phase diagram. 
It presents an even-odd asymmetry in the Mott insulator lobes. 
Some transitions are first order, others are second order and 
the character of the transitions can change with the temperature. 
It could be the ideal playground to look for a supersolid phase.


05/15/09 Armin Rahmani: "Quantum dimers on the square lattice"
	 (SCI 328 11:00am)
Abstract:
I'll introduce the Rokhsar-Kivelson (RK) quantum dimer model on the 
square lattice. After motivating the problem, I'll discuss the zero 
temperature phase diagram of the model. Focusing on the special RK point, 
I'll present a derivation of the associated continuum field theory 
through a height model representation. I will then use the field theory 
to study the quantum phase transition at the RK point.


04/24/09 Kaca Bradonjic: "Conformal and projective structures
	 of a pseudo-Riemannian manifold and their physical 
	 interpretation. Part II" (SCI 328 4:00pm)


04/16/09 Kaca Bradonjic: "Conformal and projective structures
	 of a pseudo-Riemannian manifold and their physical 
	 interpretation. Part I" (SCI 328 4:00pm)
Abstract:
Conformal and projective structures are generalizations of the metric
and the connection familiar from the general theory of relativity.
These structures are interesting as they have a clear physical
interpretation. While the conformal structure on a manifold can be
defined by a null cone at every point, the projective structure can be
defined by the set of all unparametrized paths of massive particles
through every point. I will introduce the conformal and projective
structures and discuss how one recovers full pseudo-Riemannian manifold
of general relativity by introducing these two structures on a differential
manifold and imposing two compatibility conditions between them.
While most of the talk will be a review of what has already been done 
by others, I will end with a discussion of the importance of these 
structures may have in physics and my current work in this subject.



12/17/08 Luca D'Alessio: "Quantum Hall Effect(s)"
	 (SCI 328 4:30pm)
Abstract:
I am not an expert but recently I have gone trough a lot of papers about
the Quantum Hall Effect. I think it is a very cool topic and other people
could be interested as well.

I'll try to make the point that there are many many many different types
of quantum hall effects: integer, half-integer and fractional (and among
the fractional many different types of fractions). My goal is to give you
a "survival-kit" of papers and going in some details into the explanation
of the integer quantum hall effect. I would like to review:
1) the cleanest derivation of the quantum hall effect in terms of basic
quantum mechanics. MacDonald PRB 29, 1616 (1984)
2) the physical intuition in terms of unidirectional conducting channels
along the edges (Landauer approach)
3) the explanation of the exact quantization in terms of gauge invariance
and Chern numbers. Halperin PRB 25, 2185 (1982)

If any time is left I'll say something about the fractional quantum hall
effect.



10/24/08 Alex Petersen: "'One-hit Wonders' and 'Iron-Horses': 
	 A model of Career Longevity in Professional Sports"
	 (SCI 328 5:00pm)
Abstract:
In this talk, I will provide an exactly solvable stochastic process 
for the empirical probability density functions (pdf) describing career
longevity in several professional sports leagues in various countries. 
The resulting power-law pdfs are characterized by two parameters, alpha 
and tau. The exponent alpha <= 1 defines the scaling in the power-law
regime, which is followed by an exponential cutoff after a critical 
value tau, representing the mean lifetime in each sport. 
Furthermore, alpha has a direct physical interpretation, as it quantifies 
the role of experience and reputation early in career development. 
Also, because net career tallies of in-game successes (such as home-runs 
or strikeouts) ultimately serve as a metric for classifying careers, 
the pdfs of career metrics provide a robust method for establishing 
milestones surpassed only by statistically exceptional players.


10/08/08 Joel Tanenbaum: "A Network Model of 
	 Earthwake Correlations" (SCI 328 4:30pm)
Abstract:
In our extremely preliminary research, we propose a network
to explain and model earthquake events in time and space.


09/17/08 James McNerney: "Network Properties of 
	 Input-Output Tables" (SCI 328 4:30pm)
Abstract: 
An input-output table is a matrix of data collected by nations 
describing the flows of goods between different sectors of an 
economy. The data describes an economy as a directed network, 
but no one has applied network analysis to them. 
In my presentation I introduce these networks, mention some 
basic properties, and describe some problems unique to studying 
these kinds of networks.



last modified: May 14, 2009